Generally, in an optical fiber amplifier or an optical fiber gyroscope, a lengthy optical fiber is used as an amplifying device and a detecting device thereof.
For the lengthy optical fiber, a case occurs in that an optical fiber coupler needs to be provided to perform synthesizing processing and dividing processing. The lengthy optical fiber coupler is formed such that a sidewall of an optical fiber is spliced to a sidewall of another optical fiber according to, for example, a method of abrasion extention or mechanical splice.
A device formed by combining a lengthy optical fiber and an optical fiber coupler, as described above, will be described in detail with reference to various example optical fiber amplifiers shown in FIGS. 25 to 27. The optical fiber amplifier shown in FIG. 25 is of a known forward pumping type. In this amplifier, pumping light is entered from the input side of signal light that is fed to an amplification optical fiber.
Referring to FIG. 25, reference numeral 1 denotes an amplification optical fiber. The amplification optical fiber 1 directly amplifies signal light by using stimulated output effects. Reference numeral 2 denotes an pumping light source generating pumping light that excites the amplification optical fiber 1. The pumping light source 2 is formed of, for example, a laser diode. Reference numeral 4 denotes an optical fiber coupler sending the pumping light to the amplification optical fiber 1. Reference numerals 6a and 6b individually denote isolators 6a and 6b passing the signal light only in the unidirection. The isolator 6a and 6b each perform pass through restricting processing for the signal light to prevent parasitic oscillation attributable to end face reflection and to thereby reduce noise. Reference numeral 8 denotes a bandpass filter, which is shown of removing noise component light and thereby passing only signal light. Reference numerals 10a and 10b denote an input connector and an output connector, respectively.
In the above described configuration, for example, a 1.55-μm wavelength signal light to be input on the connector 10a is passed through the isolator 6a and the optical fiber coupler 4 and is then input on the amplification optical fiber 1. Concurrently, pumping light (for example, 1.48-μm wavelength light) output from the pumping light source 2 is input on the amplification optical fiber 1 via the amplification optical fiber 1.
The amplification optical fiber 1 is excited by the pumping light and is thereby brought into a inversion state. When the signal light is input on the amplification optical fiber 1 in the aforementioned state, the amplification optical fiber 1 amplifies the signal light according to the stimulated output. The amplified signal light is passed through the isolator 6b and the bandpass filter 8, and is then emitted from the output connector 10b. 
An optical fiber amplifier shown in FIG. 26 is of a known bidirectional pumping type. In this amplifier, pumping light is entered from both the input and output sides of the signal light that is fed to the amplification optical fiber 1. Optical fiber couplers 4a and 4b are provided respectively before and behind the amplification optical fiber 1; and pumping light sources 2a and 2b are provided respectively before and behind the amplification optical fiber 1.
An optical fiber amplifier shown in FIG. 27 is of a known double stage exciting type. In this amplifier, two amplification optical fibers 1c and 1d are serially connected, and pumping light sources 2c and 2d are provided respectively for the amplification optical fibers 1c and 1d via optical fiber couplers 4c and 4d. 
In the optical fiber amplifiers shown in FIG. 25 to 27, lengthy optical fibers are used for the amplification optical fibers 1, 1c, and 1d to individually obtain predetermined amplifier gains without causing deterioration in material properties of the amplification optical fibers 1, 1c, and 1d. When assembling the optical fiber amplifier by the aforementioned lengthy optical fibers, individual optical components need to be integrated at a highest possible structural density for storing into the device.
Ordinarily, the optical fiber coupler 4, 4a, 4b, 4c, or 4d is formed in the following manner to form the amplification optical fiber 1, 1c, or 1d to be an integrated form. The amplification optical fiber is wound about a small bobbin (not shown). Other optical fibers are abrasion spliced to the end portions of the amplification optical fibers 1, 1c, or 1d wounded on the small bobbin. The optical fiber coupler 4, 4a, 4b, 4c, or 4d is formed by abrasion splicing other optical fibers to the end portions of the amplification optical fibers 1, 1c, or 1d. 
The optical fiber coupler 4, 4a, 4b, 4c, or 4d needs to be disposed along a straight line. As such, the optical fiber coupler 4, 4a, 4b, 4c, or 4d cannot be wound about the winding bobbin of the amplification optical fibers 1, 1c, or 1d. For this reason, the optical fiber coupler 4, 4a, 4b, 4c, or 4d is independently mounted in a portion near the bobbin and is then immobilized therein.
However, when the bobbin is used, and in addition, the optical fiber coupler 4, 4a, 4b, 4c, or 4d are fixed, the configuration area becomes voluminous; and as such, miniaturization cannot be cannot be implemented, and problems occur in that much time is required for, for example, wiring and disposal of the components.